I have a Rock-weed/Artillery plant and some leaves...

[Weepingfig]

I've had a rock-weed plant for about 3 or 4 months now and its has been growing wonderfully. For some reason over the last week there are some leaves that are just falling off and lading all over my desk. I have looked it over for insects, none. Checked water levels...normal. So why is it shedding leaves? Does it normally shed off old leaves like this every now and then or?